fix: create the file passed on the command line when it is missing

A path that did not exist was silently ignored: plotzilla
new-script.fountain opened an untitled document instead of a new
script saved to that file on the first save.

CHANGELOG.md

@@ -15,6 +15,8 @@ version is in the `VERSION` file.
 
 ### Fixed
 
+- `plotzilla new-script.fountain` opens a new script that will be saved to that file,
+  instead of an untitled document that forgot the name it was given.
 - The unsaved-changes marker is now updated atomically: an edit landing while a save
   finished could make the close confirmation unreliable.
 - Saving is now durable: the file is synced to disk before it replaces the old one (a